Impellers for comminutors



Filed March 6, 1962 FIG. 2

United States Patent 3,ll8,6l4 IMPELLERS FER fiflMMlNUTGRS Ludwig Johannes Meyer, Munster, Westphalia, Germany, assignor to Hazemag, Munster, Westphalia, Germany Filed Mar. 6, H62, Ser. No. 177,770 Claims priority, application Germany Mar. '7, T361 8 (Ilaims. (til. 241-493) The present invention relates to cornminuting mills in which material which is to be comminuted is engaged by a rotary impeller so as to be cornminuted either by impact with comminuting elements of the impeller itself or by being thrown upon engagement with the impeller elements toward comminuu'ng elements which are arranged about the rotary impeller.

In particular, the present invention relates to the impeller of such a comminuting apparatus.

One of the objects of the present invention is to provide an impeller of the above type which is composed of a relatively small number of rugged elements capable of being easily assembled together and wherein this small number of elements includes pluralities of these elements which are identically constructed so that the number of difierently constructed parts of the impeller of the invention is extremely small and in this way the cost is greatly reduced.

A further object of the present invention is to provide a comminutor impeller with elongated comminuting bars which are of an exceedingly simple construction so that even though these bars are made of a relatively expensive wear-resistant material it is still not difiicult to provide these bars with the simple configuration of the invention.

An additional object of the present invention is to provide an impeller of the above type which does not require any fastening structure to fasten the comminuting bars to the impeller body while at the same time guaranteeing that these comminuting bars have a fixed relationship with respect to the impeller body during rotation thereof. Thus, with the structure of the invention it is unnecessary to use any threaded bolts or the like which become exceedingly difficult to turn because of the nature of the stresses to which the impeller is subjected and the material which is comminuted and instead with the structure of the invention when the impeller does not rotate the comminuting bars thereof are so loosely connected to the impeller body that it is a simple matter to reposition the comrninuting bars or to replace them.

It is furthermore an object of the present invention to provide an impeller of the above type which is required to rotate at high speed and which nevertheless will reliably retain the comminuting bars in predetermined operating positions where they will perform the comminuting functions while at the same time rendering the bars easily removable when the impeller is stationary.

An additional object of the present invention is to provide a construction of the above type which enables the comminuting bars to be used until only an exceedingly small amount thereof remains so that the most economical use is made of these comminuting bars of the invention.

It is furthermore an object of the present invention to provide an impeller of the above type wherein the comminuting bars engage the material to be comminuted in such a way that the forces which act on these bars as a result of engagement with this material acts on the bars to urge them against the same surfaces that these bars engage as a result of centrifugal force which acts on the bars during rotation of the impeller.

With the above objects in view the invention includes, in a rotary impeller for a comminutor or the like, a rotary shaft and a pair of plates fined to said shaft for rotation therewith and spaced therealong, these plates being 10- 3,998,6l4 Patented July 23, 1963 cated respectively in planes normal to the shaft and each plate being formed with a plurality of radial notches extending inwardly from its outer circumference and distributed uniformly about the shaft. When the shaft and the plates therewith rotate in a predetermined direction, one of the side surfaces of each notch trails in this direction of rotation, and each plate is formed at least in the trailing side surface of each notch with a circumferential notch. The radial circumferential notches of the pair of plates are respectively aligned with each other and these notches permit elongated comminuting bars to be insorted through the notches into positions extending parallel to the shaft, and each comminuting bar has a rib which is located in the trailing notch of the radial notch through which the bar passes. A plurality of spacers extend between and are fixed to the plates, these spacers extending parallel to the shaft, and the spacers provide lips against which the bars press as a. result of the centrifugal force which acts on the bars during rotation of the impeller in the above direction, so that with this construction the bars will be retained in secure positions during rotation of the impeller.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a partly sectional end view of an impeller according to the present invention; and

FIG. 2 is a fragmentary sectional view taken along line lI-ll of FIG. 1 in the direction of the arrows.

Referring now to the drawings, the impeller of the invention includes a pair of rigid end plates ill formed at their central portions, respectively, with central openings through which a rotary shaft of the comminutor passes in the manner shown in FIG. 1. This shaft is of course adapted to be driven from any suitable drive during use of the impeller, and the pair of plates 10 are fixedly keyed to the shaft 11 so as to be compelled to rotate therewith.

A plurality of elongated spacers 12 extend parallel to the shaft 11 between the pair of end plates 10 of the impeller. Each plate 10 has uniformly distributed about its axis a plurality of openings which respectively receive the pins 13. As is apparent from FIGS. 1 and 2, each spacer 12 is in the form of an elongated hollow body which is closed at both of its ends, and a pair of coaxial pins 13 are respectively fixed to the end walls of each spacer 12, and these pins .13 are respectively received in the openings of the plates 10, as shown in the drawing. As is apparent from FIG. 1, the spacers 12 are spaced from the shaft 11 and have forwardly and rea-rwardly extending flanges adjacent to the shaft 11, with the flanges 20' of one spacer 12 engaging the flanges 20 of the adjoining spacers 12. These spacers 12 determine the distance between the plates 10, and when the spacers 12 are assembled with the plates 10, the spacers are welded to each other and are also welded to the plates 10 so as to form a unitary impeller body therewith this welding being provided, as indicated at 2% in FIG. 1, at the places where the spacers adjoin each other, and of course additional welding is provided at the places where the spacers engage the plates 10. Thus, it will be seen that the rotary impeller body of the invention is made up of a relatively small number of rugged parts, and of this small number of parts the several spacers 12 have an identical construction and of course the pair of plates 10 have an identical construction, so that the impeller is exceeding economical to construct, particularly according to mass production methods. It should be noted that the welding o of the spacers to the plates is provided particularly at the openings in which the pins 13 are located.

Each of the plates 10- is formed with -a plurality of radial notches 14- extending inwardly from its outer periphery and uniformly distributed about the shaft 11, and in the illustrated example there are six such notches 14 formed in each plate 119. The notches 14 are all identical with each other, and the notches 14 of one plate 111 are aligned with the notches 14 of the other plate 10. When the impeller of the invention is driven it will rotate in one direction and this direction of rotation is counterclockwise, as viewed in FIG. 1, and as is shown by the arrow Y. In this direction of rotation, each notch 14 has a trailing side and a leading side, and the trailing I side surface of each notch 14 is formed with a circumferential notch 15 while the leading side of each notch 14 is formed with a circumferential notch 16. The circumferential notches 15 and 16 of each plate 113 are also aligned with each other. As is apparent from the upper part of FIG. 1, each spacer 12 has a leading lip 31 extending along the upper edge of each trailing circumferential notch 15 and a trailing lip 19 extending along the edge of each leading notch 16 which is nearest to the shaft 11. The arrangement of the spacers 12 with respect to the notches is such that these notches are not obstructed by the spacers 12 so that it is possible to insert elongated comminuting bars 21 longitudinally of the shaft 11 through the notches in the plates so that these comminuting bars 21 may extend longitudinally of the impeller while being distributed about the shaft 11. As is apparent from FIG. 1, the several circuferential trailing notches 15 are located at a greater radial distance from the shaft 11 than the leading circumferential notches 16. The comminuting bars 21 will, in a manner described below, press against the leading lip of one spacer 12 and the trailing lip 19 of the adjoining spacer 12, and these lips which are engaged by the comminuting bars 21 may be provided with wear-resistant strips such as the angle iron 18 which is shown in the drawing welded to the lip 30. A similar wear-resistant strip 18' made of a high quality steel, for example, may be connected to the trailing lip 19 of each spacer 12.

The elongated comminuting bars 21 are slipped through the several notches in the manner shown in FIG. 1, and because of the relatively large clearance provided for the comminuting bars 21 in these notchesit is a simple matter to slip the comminuting bars into place in the stationary impeller body. The comminuting bars 21, when they are assembled with the impeller body extend along substantially the entire length thereof and have their ends located just inwardly of the outer side faces of the plates 10, and any suitable means may be provided for preventing axial movement of the comminuting bars 21 once they are assembled in this way with the impeller. Thus, for example, as is shown at the right in FIG. 1, a strip 32 may be pivotally connected at 33 to each plate 10 extending across each of the notches 14 thereof in the position of the strip '32 shown in FIG. 1, and at its outer free end the strip 32 is formed with a notch 34 which is adapted to receive a stationary pin 35. The frictional resistance to turning of the strip 32 on the pin 33 is such that the strip 32 will frictionally remain in the position in which it is turned by the operator, and in any event it will be seen that due to rotation of the impeller the strip 32 will tend to swing outwardly so that it will bear against the pin 35 and thus will remain due to centrifugal force in the position where it will revent axial movement of the comminuting bar 21. Whenever it is desired to remove .a comminuting bar, however, it is a simple matter for the operator simply to turn the strip 32 in a clockwise direction, as viewed in FIG. 1, to a position where it extends substantially radially from the pin 33 toward the shaft 11, land in this position it is out of alignment with the notch 14 which it extends across in the position shown in FIG. 1, so that in this simple way i it is possible to easily remove a comminuting bar 21. It is to be understood that elements such as the strip 32 extend across each of the slots 14 at the outer sides of the plates to.

Each of the comminuting bars 21 is made of an expensive meta-l which is particularly adapted to withstand the forces encountered during comminuting, and the hardness of this metal is such that it is difiicult to machine and it is therefore difiicult to provide comminuting bars of this metal with complex configurations. It will be see that the comminuting bars 21 used in the impeller of the invention are, in accordance with the invention, of an extremely simple configuration making it relatively easy to provide the bars 21 of the invention even though they are of this special material which is extremely resistant to the wear encountered due to the comminuting action. Thus, it will be seen that each comminuting bar 21 is in the form of an elongated substantially flat member formed in each of its side surfaces with a depression from which a rib 23 extends beyond the side surface of the bar 21. Thus, as is shown at 22 the depressions in the opposed side surface of each bar 21 makes the bar relatively narrow at 22, and from the base of each depression extends a transverse rib 23. It is a particular feature of the invention that the comminuting bars 21 are symmetrical both with respect to a plane parallel to and passing between its opposed side surfaces as well as with respect to a plane passing through the ribs 23 perpendicularly to the side surfaces, so that the comminuting bar 21 is symmetrical with respect to both of these mutually perpendicular planes.

As is particularly apparent from FIG. 2, the wearresistant steel strip 18 extends all the way across the impeller from one plate to the other, and the same is true of all of the strips 18 as well as any additional strips such as those which may be provided on the trailing lips 19 of the spacers 12. It will be seen that with this construction, one rib 23 trails and the other rib 23 leads in the direction of rotation Y shown in FIG. 1.

During rotation of the impeller in the direction of arrow Y, due to centrifugal force the several comminuting bars 21 will tend to fly outwardly away from the shaft 11. This will cause the trailing ribs 23 to press against the strips 18 carried by the leading lips 30 of the spacers 12. Thus, considering the uppermost comminuting bars 21 shown in FIG. 1, it will be seen that their trailing ribs are urged outwardly into engagement with those surfaces of the strips 18 which are directed toward the shaft 11. Due to the location of the center of gravity of each bar 21, when its trailing rib engages the strip 18 the bar will tend to turn in a direction which will press it against the leading lip 19 of the adjoining spacer 12. Thus, referring to the comminuting bar 21 shown at the upper right of FIG. 1, the trailing rib 23 thereof is pressed against the strip 18 shown at the upper right of FIG. 1, and as a result the entire bar 21 tends to turn in a clockwise direction, as viewed in FIG. 1, so that this bar 21 at the upper right of FIG. 1 presses against the trailing lip 19 of the spacer 12 shown at the uppermost part of FIG. 1. It

It will be noted that as a result of this action the leading rib 23 of each bar 21 is spaced from the lip 19, and it is only the trailing surface of each lip 19 which is engaged l by the bar 21. In fact, as a result of this particular mounting of the comminuting bars 21 according to the invention, they will engage during rotation of the impeller only the strips 18 with trailing ribs and the lips 19 with their portions located adjacent the leading ribs 23 at the side thereof directed toward the shaft 11, and except for this there will be no engagement with other parts of the impeller. With this construction the centrifugal force acting on the bars 21 is used to maintain them in the position illustrated in FIG. 1, and even during extremely high speed rotation of the impeller of the invention these bars 21 will securely remain in the positions illustrated.

The material g which is comminuted is indicated diagrammatically in FIG. 1 in engagement with a pair of the comrninuting ribs 21. It will be noted that the material to be comm-muted is engaged by the bars 21 only at their portions which extend outwardly beyond the outer surfaces of the lips 19. As may be seen from the comminuting bar 21 at the upper right of FIG. 1, for example, when the comminuting bar engages the material g, the force which acts on the bar 21 as a result of engagement with the material to be comminuted tends to position the bar 21 in exactly the same way that it is positioned according to the centrifugal forces acting on the bar 21. Thus, the impact resulting from engagement of each bar 21 with the material g will tend to also turn the bar 21, shown at the upper right of FIG. 1, for example, in a clockwise direction about the place where it engages the strip 18 so as also to press the bar against the trailing lip 19, and in this way there is no vibration or chattering of the comminuting bars when they engage the material to be c-omminuted and these comminuting bars remain securely without any vibrations in the positions where they engage the impeller body as a result of the centrifugal force resulting from rotation of the impeller body, and thus a relatively smooth, vibration-free operation is provided. In this way undersirable wear which might result from rubbing of the comminuting bars with respect to the impeller body during impact between these bars and the material to be comminuted is avoided.

On the other hand, as soon as the impeller comes to rest the comminuting bars 21 can be easily removed because of their loose connection with the impeller. There are no bolts or other fastening elements used to fix the corn-minuting bars to the impeller, so that when the impeller is stationary it is an extremely simple matter to quickly and easily remove any one of the bars 21.

Of course, during continued use of the comminuting apparatus the comminuting bars 21 will become gradually worn away. During use of the impeller the finely comminuted material k will settle onto and cover the leading rib 23 of each bar 21, so that in this way this leading rib and the central portion of each comminuting bar is protected against wear at the portion of each cornminuting bar which is exposed above each trailing lip 19 of each spacer 12. The wearing away of the outwardly extending exposed portions of the cornminuiting bars 21 will take place until, for example, each bar 21 has a surface s as shown for the upper right comminuting bar 21 in FIG. 1. It is then possible to reverse the position of each bar 21 end for end, so that in this way the comminuting bar 21 will continue to present a relatively sharp edge to the material to be comminuted, and this factor may be of importance with certain materials which are to be comminuted. it should be noted that it is possible to use each comminuting bar 21 until it is Worn to the extent indicated by the dotted line t for the upper right bar 21 of FIG. 1, and then the entire bar 21 can be removed and replaced so that the inner portion of the bar 21 which is located between the ribs 23 and the shaft 11, in the position shown in FIG. 1 will now extend outwardly beyond the plates lttl so as to be used for comminution purposes. As a result of the two perpendicular planes of symmetry described above for each bar 21, this end for end reversal and edge for edge reversal permits each comminuting bar Zll to be used until there remain only a relatively small fraction of the original bar 21, this fraction including, of course, the pair of ribs 23 and the portion of the bar 21 which extends beyond the pair of ribs 23 to the extent indicated 'by the line 1 in FIG. 1. Of course, when dealing with certain materials where a high degree of efficiency is required in the cornminuting action, it may not be economically feasible to use each bar 21 beyond the point where it has worn to the extent indicated by the dotted line s, but where the nature of the material is such that the loss of efficiency is not of too great significance, it is possible to continue to use each comminuting bar 21 until it is worn away to the extent indicated by the line 1, and this of course applies to each part of the bar 21 which is located on the opposite sides of the ribs 23.

It is apparent that the impeller of the invention is made of a relatively small number of rugged parts, and this small number of parts includes a plurality of identically constructed parts, so that only an extremely small number of differently constructed elements are required. Thus, the pair of plates lit) are identical with each other, the plurality of spacers 1-2 are identical with each other, and a plurality of comminuting bars 21 are identical with each other, and the impeller requires only two plates 10, six spacers l2, and six comminuting bars 21, in the example illustrated, so that it is clear that the impeller of the invention is extremely economical .to manufacture while being very rugged and while permitting an extremely simple, quick exchange of the comminuting bars 21 either for new comminuting bars or to be repositioned. Also, even though the impeller of the invention rotates at an extremely high speed, the several comrninuting bars 21, in spite of their loose connection with the impeller, remain securely joined thereto during operation.

it will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of comminutors differing from the types described above.

While the invention has been illustrated and described as embodied in impellers for cornminutors, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features, that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. In an impeller for com-minutors and the like, in combination, a rotary shaft; a pair of plates fixed to said shaft for rotation therewith and respectively located in planes normal to said shaft, said plates being spaced from each other and each formed with a plurality of radial notches extending inwardly from the outer periphery of each plate and distributed about said shaft, each of said notches having a side surface which trails in a predetermined direction of rotation of said shaft and plates therewith and said plates being formed at each of said radial notches with a circumferential notch at said trailing side face thereof, all of the notches of one plate :being aligned respectively with the notches of the other plate; and a plurality of elongated spacers extending parallel to said shaft and located between and fixed to said plates to determine the distance therebetwcen, said spacers also being fixed to each other so as to form with said plates and shaft a unitary impeller body, said spacers being out of line with said notches, said plurality of spacers respectively having elongated trailing portions extending parallel to the shaft axis and located adjacent said circumferential notches, respectively and elongated leading portions located ahead of said trailing portions, respectively, in the direction of rotation of said shaft and also located nearer to said axis than said trailing portions.

2. In an impeller for comminutors and the like, in combination, a rotary shaft; a pair of plates fixed to said shaft for rotation therewith and respectively located in planes normal to said shaft, said plates being spaced from each other and each formed with a plurality of radial notches extending inwardly from the outer periphery of each plate and distributed about said shaft, each of said mine the distance therebetween, said spacers also being fixed to each other so as to form with said plates and shaft a unitary impeller body, said spacers being out of line with said notches, and each of said spacers being in the form of an elongated, closed, hollow element, said plurality of spacers respectively having elongated trailing portions extending parallel to the shaft axis and located adjacent said circumferential notches, respectively, and elongated leading portions located ahead of said trailing portions, respectively, in the direction of rotation of said shaft and also located nearer to said axis than said trailing port-ions.

3. In an impeller for comminutors and the like, in combination, a rotary shaft; a pair of plates fixed to said shaft and spaced from each other there-along, said plates being located respectively in planes normal to said shaft and each plate being formed with a plurality of substantially radial notches extending inwardly from is outer periphery and distributed about said shaft as well as with a plurality of openings also distributed about said shaft, and each of said notches having a side surface which trails in a predetermined direction of rotation of said shaft, said plates being for-med in each of said side surfaces of said notches thereof with a circumferential notch; and a plurality of elongated, hollow, closed spacer bodies extending axially of said shaft and located between said plates to determine the distance therebetween, said bodies respectively having end walls fixedly carrying pins which are respectively located in said openings of said plates, said plurality of spacers respectively having elongated trailing portions extending parallel to the shaft axis and located adjacent said circumferential notches, respectively, and elongated leading portions located ahead of said trailing portions, respectively, in the direction of rotation of said shaft 'and also located nearer to said axis than said trailing portions.

4. In an impeller for comminutors and the like, in combination, a rotary impeller body having a pair of end plates and a plurality of elongated spacer means extending between and connected to said end plates to determine the spacing therebetween, said plurality of elongated spacer means extending parallel to the axis of rotation of the impeller body and said pair of plates being respectively formed with substantially radial notches extending inwardly from their outer peripheries, distributed about said axis, and the notches of one plate being aligned with those of the other plate, each of said notches having a trailing side surface which trails in the direction of rotation of the gated trailing portions extending parallel to said axis and located adjacent said circumferential notches, respectively,

and elonagted leading portions located ahead of said trailing portions, respectively, in the direction of rotation of the impeller body and also located nearer to said axis than said trailing portions; and a plurality of elongated cornminuting bars respectively extending between said end plates parallel to said axis and being introduced through said radial and circumferential notches, each bar having a trailing rib located in said circumferetnial notch and urged by centrifugal force outwardly against said trailing portion of said plurality of spacer means, the engagement of said rib with said trailing portion of each of said spacer means tending to turn each bar in a direction which maintains said bar pressed against said leading portion of each of said plurality of spacer means during rotation of said impeller body, whereby said bars are maintained by centrifugal force in predetermined positions with respect to said end plates and plurality of spacer means during rotation of the impeller body While at the same time when the latter does not rotate said bars are loosely carried and can be easily removed to have their positions changed or to be replaced.

5. In an impeller for comminutors and the like, in combination, a rotary impeller body having a pair of end plates and a plurality of elongated spacer means extending between and connected to said end plates to determine the spacing therebetween, said plurality of elongated spacer means extending parallel to the axis of rotation of the impeller body and said pair of plates being respectively formed with substantially radial notches extending inwardly from their outer peripheries, distributed about said axis, and the notches of one plate being aligned with those of the other plate, each of said notches having a trailing side surface which trails in the direction of rotation of the impeller body and said plates being formed in each of said trailing side surfaces with a circumferential notch, said plurality of spacer means respectively having elongated trailing portions extending parallel to said axis and located adjacent said circumferential notches, respectively, and elongated leading portions located ahead of said trailing portions, respectively, in the direction of rotation of the impeller body and also located nearer to said axis than said trailing portions; a plurality of elongated comminuting bars respectively extending between said end plates parallel to said axis and being introduced through said radial and circumferential notches, each bar having a trailing rib located in said circumferential notch and urged by centrifugal force outwardly against said trailing portion of said plurality of spacer means, the engagement of said rib with said trailing portion of each of said spacer means tending to turn each bar in a dircction which maintains said bar pressed against said leading portion of each of said plurality of spacer means during rotation of said impeller body, whereby said bars are maintained by centrifugal force in predetermined positions with respect to said end plates and plurality of spacer means during rotation of the impeller body while at the same time when the latter does not rotate said bars are loosely carried and can be easily removed to have their positions changed or to be replaced; and elongated wearresisting means carried by said plurality of spacer means respectively at said trailing portions thereof.

6. In an impeller for comminutors and the like, in combination, a rotary impeller body having a pair of end plates and a plurality of elongated spacer means extending between and connected to said end plates to determine the spacing there'between, said plurality of elongated spacer means extending parallel to the axis of rotation of the impeller body and said pair of plates being respectively formed with substantially radial notches extending inwardly from their outer peripheries, distributed about said axis, and the notches of one plate being aligned with those of the other plate, each of said notches having a trailing side surface which trails in the direction of rotation of the impeller body and said plates being formed in each of said trailing side surfaces with a circumferential notch, said plurality of spacer means respectively having elongated trailing portions extending parallel to said axis and located adjacent said circumferential notches, respectively, and elongated leading portions located ahead of said trailing portions, respectively, in the direction of rotation of the impeller body and also located nearer to said axis than said trailing portions; a plurality of elongated comminuting bars respectively extending between said end plates parallel to said axis and being introduced through said radial and circumferential notches, each bar having a trailing rib located in said circumferential notch and urged by centrifugal force outwardly against said trailing portion of said plurality of spacer means, the engagement of said rib with said trailing portion of each of said spacer means tending to turn each bar in a direction which maintains said bar pressed against said leading portion of each of said plurality of spacer means during rotation of said impeller body, whereby said bars are maintained by centrifugal force in predetermined positions with respect to said end plates and plurality of spacer means during rotation of the impeller body while at the same time when the latter does not rotate said bars are loosely carried and can be easily removed to have their positions changed or to be replaced; and means carried by said plates for releasably preventing axial movement of said bars once they are located on the impeller body.

7. in an impeller for comminutors and the like, in combination, a rotary shaft; a pair of plates fixed to said shaft for rotation therewith and spaced therealong, said plates being respectively located in planes normal to said shaft and each plate being formed with a plurality of substantially radial notches extending inwardly from its outer periphery and uniformly distributed about said shaft with the radial notches of one plate aligned respectively with the radial notches of the other plate, and each notch having one side surface which trails in a predetermined direction of rotation of said shaft and plates and an opposite side surface which leads in said direction of rotation, each plate being formed in each of its notches with a pair of circumferential notches extending inward from said side surfaces of each notch with the circumferential notch extending from the leading side surface of each notch located closer to said shaft than the circumferential notch extending from the trailing side surface of each radial notch, and all of said circumferential notches of one plate being respectively aligned with the circumferential notches of the other plate; a plurality of elongated spacers extending parallel to said shaft, distributed thereabout, and extending between and fixed to said plates to determine the space therebetween, said spacers respectively having leading lips which lead in said direction of rotation and which extend respectively along said trailing circumferential notches at portions thereof which are located most distant from said shaft and said spacers respectively having trailing lips which trail in said direction of rotation and which respectively extend along those portions of said leading circumferential notches which are nearest to said shaft; and a plurality of comrninuting bars respectively located in radial planes which extend radially with respect to said shaft and extending parallel to the latter, each of said bars extending outwardly beyond said plates and located between the trailing lip of one spacer and the leading lip of the next following spacer and each bar having a pair of side ribs which can pass with clearance through said circumferential notches, one of said side ribs of each bar trailing in said direction of rotation and being urged by centrifugal force against said leading lip of a spacer adjacent to said bar and the other rib leading in said direction and being spaced from the trailing lip of the spacer located on the leading side of said bar, the centrifugal force which acts on said bar tending to turn the latter about the place where said trailing rib thereof engages said leading lip of a spacer so that a portion of said bar adjacent said leading rib thereof located nearer to said shaft then said leading rib will be pressed against said trailing lip of an adjoining spacer, whereby said bars have their locations with respect to said spacers and plates determined during rotation of the impeller so that said bars will not be loosely connected to said plates and spacers during rotation of the impeller whereas when the impeller is stationary said bars are relatively loose and can easily be removed to be replaced or to have their positions changed.

8. In an impeller for comminutors and the like, in combination, a rotary impeller body being formed with a plurality of elongated openings extending in substantially radial direction from the periphery of said body toward the axis of rotations thereof and being distributed about said axis, said body having at each opening an elongated trailing portion extending parallel to said axis and forming a first abutment surface transverse to the elongation of said opening and having an elongated leading portion located ahead of said trailing portion in the direction of rotation of said body and forming a second abutment surface extending substantially in axial direction and being located nearer to said axis than said first abutment surface; and a plurality of elongated contrninuting bars projecting with free end portions thereof radially beyond said outer periphery of said body and having each an inner portion located with clearance in said openings, respectively, each bar having a trailing rib located radially inwardly of said first abutment surface and urged, during rotation of said body, by centrifugal force outwardly into engagement with said first abutment surface, the engagement of said rib with said abutment surface tending to turn each bar in a direction which maintains said bar pressed against said second abutment surface, whereby said bars are maintained :by centrifugal force in predetermined positions with respect to said impeller body which will not be changed under the impact of the material to be lcon'imin-uted onto said free end portions of said bars while at the same time said bars can be easily removed in direction of said axis from said openings when said impeller body does not rotate.

References Cited in the file of this patent UNITED STATES PATENTS 2,373,691 Kessler Apr. 17, 1945 FOREIGN PATENTS 678,428 Great Britain Sept. 3, 1952 1,015,304 Germany Sept. 5, 1957 

8. IN AN IMPELLER FOR COMMINUTORS AND THE LIKE, IN COMBINATION, A ROTARY IMPELLER BODY BEING FORMED WITH A PLURALITY OF ELONGATED OPENINGS EXTENDING IN SUBSTANTIALLY RADIAL DIRECTION FROM THE PERIPHERY OF SAID BODY TOWARD THE AXIS OF ROTATIONS THEREOF AND BEING DISTRIBUTED ABOUT SAID AXIS, SAID BODY HAVING AT EACH OPENING AN ELONGATED TRAILING PORTION EXTENDING PARALLEL TO SAID AXIS AND FORMING A FIRST ABUTMENT SURFACE TRANSVERSE TO THE ELONGATED OF SAID OPENING AND HAVING AN ELONGATED LEADING PORTION LOCATED AHEAD OF SAID TRAILING PORTION IN THE DIRECTION OF ROTATION OF SAID BODY AND FORMING A SECOND ABUTMENT SURFACE EXTENDING SUBSTANTIALLY IN AXIAL DIRECTION AND BEING LOCATED NEARER TO SAID AXIS THAN SAID FIRST ABUTMENT SURFACE; AND A PLURALITY OF ELONGATED COMMINUTING BARS PROJECTING WITH FREE END PORTIONS THEREOF RADIALLY BEYOND SAID OUTER PERIPHERY OF SAID BODY AND HAVING EACH AN INNER PORTION LOCATED WITH CLEARANCE IN SAID OPENINGS, RESPECTIVELY, EACH BAR HAVING A TRAILING RIB LOCATED RADIALLY INWARDLY OF SAID FIRST ABUTMENT SURFACE AND URGED, DURING ROTATION OF SAID BODY, BY CENTRIFUGAL FORCE OUTWARDLY INTO ENGAGEMENT WITH SAID FIRST ABUTMENT SURAFACE, THE ENGAGEMENT OF SAID RIB WITH SAID ABUTMENT SURFACE TENDING TO TURN EACH BAR IN A DIRECTION WHICH MAINTAINS SAID BAR PRESSED AGAINST SAID SECOND ABUTMENT SURFACE, WHEREBY SAID BARS ARE MAINTAINED BY CENTRIFUGAL FORCE IN PREDETERMINED POSITIONS WITH RESPECT TO SAID IMPELLER BODY WHICH WILL NOT BE CHANGED UNDER THE IMPACT OF THE MATERIAL TO BE COMMINUTED UNTO SAID FREE END PORTIONS OF SAID BARS WHILE AT THE SAME TIME SAID BARS CAN BE EASILY REMOVED IN DIRECTION OF SAID AXIS FROM SAID OPENINGS WHEN SAID IMPELLER BODY DOES NOT ROTATE. 